Method for X-ray wavelength measurement and X-ray wavelength measurement apparatus

ABSTRACT

A Method for X-ray wavelength measurement and an X-ray wavelength measurement apparatus capable of determining absolute wavelength easily and carrying out wavelength measurement having high precision with a simple structure are provided. The present invention is a Method for X-ray wavelength measurement carried out by using a channel-cut crystal for wavelength measurement ( 20 ) in which two opposing cut planes are formed and the lattice constant of which is known, and the method diffracts X-ray in respective arrangements (−, +) and (+, −) of the channel-cut crystal for wavelength measurement ( 20 ), to determine the absolute wavelength of the X-ray from the difference between crystal rotation angles in respective arrangements. This makes the alignment simpler, and, when only a channel-cut crystal suitable for measurement can be prepared, X-ray wavelength measurement can be carried out easily and with high precision.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for X-ray wavelengthmeasurement and X-ray wavelength measurement apparatus for carrying outX-ray wavelength measurement with high precision.

2. Description of the Related Art

Such an X-ray wavelength measurement apparatus for carrying out X-raywavelength measurement with high precision by using a slit to narrowdown the incident direction of X-ray, or by arranging two analyzingcrystals has been conventionally known. In addition, there is such aninstrument as allowing four analyzing crystals to be interlocked withgears in order to obtain high resolution (for example,JP-A-2005-140719).

An X-ray wavelength measurement apparatus as disclosed inJP-A-2005-140719 irradiates radiation light as primary X-ray to asample, and spectrally reflects fluorescent X-ray generated from thesample with four analyzing crystals in (+, −, −, +) arrangement tomeasure the intensity with a detector. Then, while changing thewavelength of the fluorescent X-ray spectrally reflected with theanalyzing crystals by an interlocking means for interlocking theanalyzing crystals and the detector, the apparatus guides thefluorescent X-ray into the detector. In this way, the resolution of thefluorescent X-ray spectrum is improved.

However, when such an X-ray wavelength measurement apparatus asdescribed above is used, a slit is separately used to adjust strictly adiffraction angle θ for the purpose of determining absolute wavelength.Consequently, for the alignment to adjust a standard position, a specialtechnique is required, and the measurement can not be carried outsimply. Further, an X-ray wavelength measurement apparatus oftwo-crystal arrangement, which utilizes the arrangement of two planaranalyzing crystals, needs an interlocking mechanism and results in acomplex structure.

SUMMARY OF THE INVENTION

The present invention is achieved with the view of such circumstances,and aims to provide a method for X-ray wavelength measurement and anX-ray wavelength measurement apparatus for easily determining absolutewavelength and carrying out precise wavelength measurement with a simplestructure.

(1) In order to attain the above objects, the method for X-raywavelength measurement according to the present invention is a methodfor X-ray wavelength measurement carried out by using a channel-cutcrystal for wavelength measurement on which two opposing cut planes areformed and the lattice constant of which is known, and the method ischaracterized by comprising the steps of: diffracting X-ray inrespective arrangements of (−, +) and (+, −) with the channel-cutcrystal for wavelength measurement; and determining the absolutewavelength of X-ray from the difference between crystal rotation anglesin the respective arrangements.

As described above, in the Method for X-ray wavelength measurement ofthe present invention, by diffracting and spectrally reflecting X-ray inrespective arrangements (−, +) and (+, −) of the channel-cut crystal forwavelength measurement, it is possible to determine the zero point ofthe crystal rotation angle. Consequently, as compared with theconventional method which requires precise position adjustment by usinga slit, the alignment becomes simpler. As the result, when only achannel-cut crystal suitable for measurement can be prepared, themeasurement can be carried out easily with high precision.

(2) The Method for X-ray wavelength measurement according to the presentinvention is the Method for X-ray wavelength measurement, carried out byusing a channel-cut crystal for collimator which is arranged on an X-rayincident side of the channel-cut crystal for wavelength measurement andin which two opposing cut planes are formed, and the method is furthercharacterized by comprising the steps of: diffracting X-ray at a crystalplane having the same index as that of a crystal plane at which thechannel-cut crystal for wavelength measurement diffracts X-ray atrespective cut planes of the channel-cut crystal for collimator; andguiding the diffracted X-ray into the channel-cut crystal for wavelengthmeasurement to carry out wavelength measurement.

Consequently, when X-ray to be spectrally reflected is divergent light,the X-ray is diffracted in different angles for respective wavelengthsby the channel-cut crystal for collimator to enter a channel-cut crystalfor wavelength measurement. As the result, it is possible to carry outX-ray wavelength measurement without interlocking the rotation of thechannel-cut crystal for collimator with the channel-cut crystal forwavelength measurement.

(3) The X-ray wavelength measurement apparatus according to the presentinvention comprises: a channel-cut crystal for wavelength measurement inwhich two opposing cut planes are so formed that at least a part ofmutual projections thereof overlap with the cut planes; and a detectorfor detecting the intensity of X-ray spectrally reflected by thechannel-cut crystal for wavelength measurement, wherein a rotationcenter of the channel-cut crystal for wavelength measurement is set tobe capable of diffracting X-ray in respective arrangements of (−, +) and(+, −).

As described above, in the X-ray wavelength measurement apparatus of thepresent invention, the channel-cut crystal for wavelength measurementhas a rotation center so set that it can diffract X-ray in thearrangement of (−, +) and (+, −). Consequently, it is possible to carryout wavelength measurement in above two arrangements to determineprecisely the diffraction angle from the difference of crystal rotationangles, and therefore the alignment becomes simpler as compared with theconventional method that requires precise position adjustment by using aslit. Further, since it is not necessary to interlock the channel-cutcrystal upon carrying out X-ray wavelength measurement, the mechanismcan be made simple. In addition, the X-ray wavelength measurementapparatus for wavelength measurement with setting two planer analyzingcrystals in (+, +) arrangement have limitation on the diffraction angleof the analyzing crystal due to the interference of respective parts ofthe instrument, but in the X-ray wavelength measurement apparatus of thepresent invention, the position of the X-ray detector does not need tobe largely moved, and, by preparing analyzing crystals suitable forrespective diffraction angles, the diffraction angle is not limited.

(4) The X-ray wavelength measurement apparatus according to the presentinvention is characterized by further comprising a channel-cut crystalfor collimator which is arranged on the incident side of the channel-cutcrystal for wavelength measurement and in which two opposing cut planesare formed, wherein the channel-cut crystal for collimator diffractsX-ray at a crystal plane having the same index as that of a crystalplane at which the channel-cut crystal for wavelength measurementdiffracts X-ray, to guide the diffracted X-ray into the channel-cutcrystal for wavelength measurement.

Consequently, when X-ray to be spectrally reflected is divergent light,the X-ray is diffracted in different angles for respective wavelengthsby the channel-cut crystal for collimator to enter the channel-cutcrystal for wavelength measurement. As the result, it is possible tocarry out X-ray wavelength measurement without interlocking the rotationof the channel-cut crystal for collimator with the channel-cut crystalfor wavelength measurement, and to make the structure of the instrumentsimple.

(5) The X-ray wavelength measurement apparatus according to the presentinvention is characterized in that the channel-cut crystal forcollimator is placed so that the rotation can be fixed for the incidentX-ray upon carrying out wavelength measurement.

As described above, it is possible to carry out X-ray wavelengthmeasurement, for a divergent light source, only by adjusting therotation of the channel-cut crystal for wavelength measurement withoutinterlocking the rotation of the channel-cut crystal for collimator withthe channel-cut crystal for wavelength measurement. Consequently, thestructure of the instrument can be made simple.

(6) The X-ray wavelength measurement apparatus according to the presentinvention is characterized in that the rotation center of thechannel-cut crystal for wavelength measurement is set between two cutplanes of the channel-cut crystal for wavelength measurement or betweenextended planes thereof; and a cut plane on which X-ray is incident whenthe channel-cut crystal for wavelength measurement diffracts the X-rayin the arrangement of (−, +) differs from that on which X-ray isincident when the channel-cut crystal for wavelength measurementdiffracts the X-ray in the arrangement of (+, −).

As described above, in the X-ray wavelength measurement apparatus of thepresent invention, the rotation center of the channel-cut crystal forwavelength measurement is set between two cut planes of the channel-cutcrystal for wavelength measurement or between extended planes thereof.Consequently, when X-ray is made diffracted in the arrangements (−, +)and (+, −) of the channel-cut crystal for wavelength measurement, it ispossible to guide X-ray into different cut planes in the respectivearrangements for wavelength measurement, and to measure absolutewavelength with high precision from the difference between respectivecrystal rotation angles even for a small diffraction angle.

(7) The X-ray wavelength measurement apparatus according to the presentinvention is characterized in that the rotation center of thechannel-cut crystal for wavelength measurement is set in a positionallowing X-ray to enter the identical cut plane when the channel-cutcrystal for wavelength measurement diffracts the X-ray in eitherarrangement of (−, +) or (+, −).

As described above, in the X-ray wavelength measurement apparatus of thepresent invention, the rotation center of the channel-cut crystal forwavelength measurement is so set that X-ray can enter the identical cutplane when the crystal diffracts the X-ray in either arrangement (−, +)or (+, −), therefore, even for high diffraction angles, absolutewavelength can be measured with high precision from the differencebetween respective crystal rotation angles. In addition, for a highdiffraction angle, δλ/λ(=δθ/tan θ) becomes small, therefore wavelengthresolution can be improved.

(8) The X-ray wavelength measurement apparatus according to the presentinvention is characterized by further comprising a rotation controlmechanism for controlling the rotation of the channel-cut crystal forwavelength measurement, wherein the rotation control mechanism includesan angle detector having self-calibration function for detecting thedisplacement of the scale position of the rotation angle.

As described above, since the X-ray wavelength measurement apparatus ofthe present invention is provided with an angle detector havingself-calibration function, it can detect the displacement of the scaleposition of the rotation angle of the channel-cut crystal for wavelengthmeasurement and calibrate absolute wavelength. Further, it can alsoevaluate how much degree of inaccuracy exists in the obtained absolutewavelength.

According to the Method for X-ray wavelength measurement of the presentinvention, since the zero point of the crystal rotation angle can bedetermined by rotating the channel-cut crystal for wavelengthmeasurement to diffract and spectrally reflect X-ray in respectivearrangements of (−, +) and (+, −), the alignment becomes simpler ascompared with the conventional method which requires precise positionadjustment by using a slit. As the result, when only a channel-cutcrystal suitable for measurement is prepared, the measurement can becarried out easily with high precision.

According to the X-ray wavelength measurement apparatus of the presentinvention, since the zero point of the crystal rotation angle can bedetermined by diffracting and spectrally reflecting X-ray in thearrangements where the channel-cut crystal for wavelength measurement isset in (−, +) and (+, −) respectively, the alignment becomes simple.Further, there is no necessity to interlock the channel-cut crystal forcollimator, thus making the mechanism simple. Furthermore, an X-raywavelength measurement apparatus with two planer analyzing crystals thatcarries out wavelength measurement in an arrangement of (+, +) haslimitation on the diffraction angle of the analyzing crystal due to theposition of the X-ray detector, but the X-ray wavelength measurementapparatus of the invention does not need large movement of the positionof the detector and is not limited by diffraction angles by preparinganalyzing crystals suitable for respective diffraction angles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing the outline of an X-ray wavelengthmeasurement apparatus of an embodiment 1.

FIG. 2A is a plan view showing a channel-cut crystal for wavelengthmeasurement in an arrangement of (+, −). FIG. 2B is a plan view showingthe channel-cut crystal for wavelength measurement in an arrangement of(−, +).

FIG. 3 is a plan view showing the outline of an X-ray wavelengthmeasurement apparatus of an Embodiment 2.

FIG. 4 is a plan view showing the outline of the X-ray wavelengthmeasurement apparatus of the Embodiment 2.

FIG. 5A is a plan view showing the channel-cut crystal for wavelengthmeasurement in an arrangement of (+, −).

FIG. 5B is a plan view showing the channel-cut crystal for wavelengthmeasurement in an arrangement of (−, +).

FIG. 6 is a side view showing the outline of an X-ray wavelengthmeasurement apparatus of an Embodiment 3.

FIG. 7 is a perspective view of an angle detector used for the X-raywavelength measurement apparatus of the Embodiment 3.

FIG. 8 is a profile showing the result of practicing a Method for X-raywavelength measurement according to the present invention.

FIG. 9 is a drawing showing parameters of respective Lorenz functions.

DETAILED DESCRIPTION OF THE INVENTION Best Modes for Carrying Out theInvention

Next, embodiments of the present invention will be described withreference to the drawings. To facilitate understanding of thedescription, the same reference numeral is given to the same constituentand overlapping description is omitted.

Embodiment 1

FIG. 1 is a plan view showing the outline of the configuration of anX-ray wavelength measurement apparatus 1 according to the presentinvention. As shown in FIG. 1, the X-ray wavelength measurementapparatus 1 includes a channel-cut crystal for collimator 10, achannel-cut crystal for wavelength measurement 20, a rotatable platform50, an angle detector 60 and an X-ray detector 100. The channel-cutcrystal is prepared by carving grooves to a unitary crystal block, andthe parallel walls on both sides thereof are utilized for reflection,that is, diffraction. For the channel-cut crystal, the whole is composedof unitary crystal, and therefore all X-rays Bragg-reflected by onecrystal wall cause Bragg reflection by the other crystal wall. The X-raywavelength measurement apparatus 1 spectrally reflects X-ray having aspecified wavelength out of incident X-ray having a continuous spectrum,and measures the intensity thereof with the X-ray detector 100. TheX-ray wavelength measurement apparatus 1 can be applied to, for example,a state analysis instrument by spectroscopy and an X-ray wavelengthprecise measuring instrument.

The channel-cut crystal for collimator 10 is arranged on the X-rayincident side of the channel-cut crystal for wavelength measurement 20,and has a first crystal wall 11 and a second crystal wall 12. Atrespective crystal walls, a first cut plane 11 a and a second cut plane12 a facing each other are formed. The channel-cut crystal forcollimator 10 is fixed on a platform (not shown) at a position whereX-ray being an object to be spectrally reflected enters to bediffracted. When X-ray to be spectrally reflected is divergent light,the X-ray is diffracted in different angles for respective wavelength bythe fixed channel-cut crystal for collimator to enter the channel-cutcrystal for wavelength measurement. Accordingly, in the X-ray wavelengthmeasurement apparatus 1, it is possible to carry out X-ray wavelengthmeasurement without interlocking the rotation of the channel-cut crystalfor collimator 10 with the channel-cut crystal for wavelengthmeasurement 20. Accordingly, the structure of the instrument can be madesimple. Further, when X-ray to be spectrally reflected is parallel lightsuch as radiation from synchrotron source, the channel-cut crystal forcollimator may be omitted to make the configuration simpler.

The Bragg angle of the channel-cut crystal for collimator 10 isrepresented as θ₁ in FIG. 1. The channel-cut crystal for collimator isso arranged that X-ray having been diffracted by the channel-cut crystalfor collimator 10 enters the channel-cut crystal for wavelengthmeasurement 20. The channel-cut crystal for collimator 10 may have suchfigure and arrangement that allow X-ray to be diffracted at a crystalplane having the same index as that of a crystal plane at which thechannel-cut crystal for wavelength measurement 20 allows X-ray to bediffracted, so that the X-ray may enter the channel-cut crystal forwavelength measurement 20. The number of diffraction at the channel-cutcrystal is at least two, may be four or six, and there is no particularlimitation on it. By increasing the number of the diffraction, a sharppeak having a cut tail can be detected. On the other hand, whenemphasizing the assurance of intensity, the number of the diffractionmay be decreased.

Incidentally, although the channel-cut crystal for collimator 10 isfixed on the platform during the spectrum measurement, it is so designedthat the adjustment of the angle prior to the measurement is possible.The adjustment may be practiced either manually or automatically. In anyevent, the channel-cut crystal for collimator 10 is independent of therotation control of the channel-cut crystal for wavelength measurement20 to be described.

The channel-cut crystal for wavelength measurement 20 has a thirdcrystal wall 21 and a fourth crystal wall 22. At respective crystalwalls, a third cut plane 21 a and a fourth cut plane 22 a facing eachother are formed. In addition, the projection of the cut plane 21 a tothe cut plane 22 a and the cut plane 22 a are so formed that at least apart of these overlap with each other. That is, when the channel-cutcrystal for wavelength measurement is viewed from the side, the crystalwalls 21 and 22 overlap with no interspace. This makes it possible torotate the channel-cut crystal for wavelength measurement 20 to diffractX-ray in respective arrangements of (−, +) and (+, −).

The arrangement of (+) or (−) indicates an arrangement of a crystal thatdiffracts X-ray in the bending direction determined by regarding thebending direction of the first diffraction as (+). Accordingly, anarrangement of a crystal that diffracts X-ray in the same bendingdirection as that in the first diffraction is (+), and an arrangement ofa crystal that diffracts X-ray in the bending direction reverse to thatof the first diffraction is (−).

In the arrangement, a rotation center C1 is set at a position wherethere occurs that X-ray reaches the both cut planes.

As described above, the rotation center C1 thereof is set in thechannel-cut crystal for wavelength measurement 20 so as to make itpossible to diffract X-ray in arrangements of (−, +) and (+, −). Asdescribed above, since it is possible to carry out the spectralreflection in the arrangement to determine the zero point of the crystalrotation angle, the alignment becomes simpler as compared with theconventional method that requires precise position adjustment by using aslit.

In an example in FIG. 1, the rotation center C1 is set between the cutplanes 21 a and 22 a. The cut plane 21 a on which X-ray is incident whenthe channel-cut crystal for wavelength measurement 20 takes the (−, +)arrangement, and the cut plane 22 a on which X-ray is incident when thechannel-cut crystal for wavelength measurement 20 takes the (+, −)arrangement are different from each other. In other words, for the cutplane 21 a, (−) diffraction occurs in either arrangement, and for thecut plane 22 a, (+) diffraction occurs in either arrangement. Here, therotation center C1 may be set between the extended planes of respectivecut planes. The Bragg angle of the channel-cut crystal for wavelengthmeasurement 20 is represented by θ₂ in FIG. 1.

Analyzing crystals that can be used for the channel-cut crystal forcollimator 10 or the channel-cut crystal for wavelength measurement 20include Si and Ge, but are not limited to these. As to crystal planesfor use in spectral reflection, for example, Si (400), Si (220), Si(440), Si (111), Si (333) and Si (444) can be mentioned. The rotatableplatform 50 is connected to a rotary driving instrument (not shown)capable of rotating at intervals of a minute angle. The rotary drivinginstrument uses a servo motor, a stepping motor or the like.

The angle detector 60 is a detector for measuring the rotation angle ofthe channel-cut crystal for wavelength measurement 20 by counting thescale carved to a circular disc with a reading head. The angle detector60 uses, for example, a common rotary encoder. The rotatable platform50, the angle detector 60 and the X-ray detector 100 are controlled by acontrolling section (not shown).

The X-ray detector 100 is arranged at apposition on which the X-raydiffracted by the channel-cut crystal for wavelength measurement 20 isincident. In the present invention, there is no need to move largely theposition of the X-ray detector to eliminate the limitation on the anglecaused by the interference of respective sections. The X-ray detector100 detects the intensity of the X-ray spectrally reflected by thechannel-cut crystal. The position of the X-ray detector 100 can be movedcorresponding to the incident position of the X-ray. Incidentally, theX-ray detector 100 may use the one having a large detection range, beingfixed and used at a predetermined position.

Next, a method for X-ray wavelength measurement by using theaforementioned X-ray wavelength measurement apparatus 1 will bedescribed. Firstly, from a crystal having a known lattice constant, twochannel-cut crystals are prepared in which a cut plane is formed so asto diffract X-ray at the identical crystal plane. One of these is set ona platform as the channel-cut crystal for collimator 10, and the otheris set on the rotatable platform 50 as the channel-cut crystal forwavelength measurement 20. Then, the channel-cut crystal for collimator10 is adjusted and fixed so as to diffract X-ray having required rangeof wavelength in the direction of channel-cut crystal for wavelengthmeasurement 20. On the other hand, the channel-cut crystal forwavelength measurement 20 is fixed on the rotatable platform 50 so thatthe rotation center C1 lies between the cut planes 21 a and 22 a. Then,the rotatable platform 50 is rotated to set the channel-cut crystal forwavelength measurement 20 in such arrangement that causes (+, −)diffraction as shown in FIG. 2A.

Subsequently, by guiding X-ray for spectral reflection, firstly,wavelength measurement is carried out in such setting that thechannel-cut crystal for wavelength measurement 20 has an arrangement of(+, −) to diffract X-ray. That is, the arrangement is set so that thediffraction by respective channel-cut crystals is (+, −, +, −), and theX-ray is diffracted in the order of cut planes 11 a, 12 a, 22 a and 21a. On this occasion, in case where diffraction is carried out by usingthe identical crystal plane for the channel-cut crystal for collimatorand for the channel-cut crystal for wavelength measurement, a sharp peakcan be obtained when two crystal planes become strictly parallel to eachother. As described above, the peak angle position ω₀ of the X-rayintensity having been detected with the X-ray detector 100 is detectedwith the angle detector 60. The peak angle position ω₀ is the originposition of the channel-cut crystal for wavelength measurement.

Next, the channel-cut crystal for wavelength measurement 20 is set to anarrangement that diffracts X-ray in (−, +) as shown in FIG. 2B. That is,respective channel-cut crystals are arranged so as to give (+, −, −, +)diffractions, respectively, and the X-ray is diffracted in the order ofcut planes 11 a, 12 a, 21 a and 22 a. Then, from the X-ray intensitydetected by the X-ray detector 100 and the angle ω detected by the angledetector 60, an X-ray spectrum with high resolution is obtained.Incidentally, the angle detected by the angle detector 60 can beobtained by measuring the rotation amount of the rotation platform orthe rotation axis (shaft) from the reference rotation position with theangle detector 60, which corresponds to the crystal rotation angle. Themethod for determining angles ω and ω₀ as shown in the drawing is anexample, and there is no particular limitation on the method fordetermining the angle when the angle represents the rotation angle ofthe crystal.

The origin of the angle ω detected by the angle detector 60 in themeasured spectrum is the above-described ω₀. Accordingly, the differencebetween both angles ω−ω₀ is the rotation angle of the channel-cutcrystal for wavelength measurement, and Bragg angle θ of the channel-cutcrystal for wavelength measurement on this occasion is represented byθ=(ω−ω₀)/2. When representing the lattice spacing of the channel-cutcrystal for wavelength measurement by d, the angle θ on the horizontalaxis of a measured spectrum can be converted to the wavelength λ ofX-ray according to the formula of λ=2d·sin θ. Further, the wavelength λ(Å) of X-ray is converted to energy E (eV) according to the formula ofE=12398.419/A.

In this way, the absolute wavelength of spectrally reflected X-ray canbe detected. As described above, X-ray is diffracted in respectivearrangements in which two channel-cut crystals are set to (+, −, −, +)and (+, −, +, −) by rotating the channel-cut crystal for wavelengthmeasurement 20 to carry out spectral reflection and determine the originof the crystal rotation angle, therefore the alignment becomes simpleras compared with conventional method that requires precise positionadjustment by using a slit. As the result, when only suitablechannel-cut crystals are prepared, X-ray wavelength measurement can becarried out easily with high precision.

Embodiment 2

In the above-described Embodiment 1, the rotation center C1 is soprovided that X-ray enters different cut planes when the channel-cutcrystal for wavelength measurement 20 is set to respective arrangementsof (+, −) and (−, +), but the rotation center may be provided so thatX-ray may enter the identical cut plane. FIG. 3 is a schematic drawingshowing the X-ray wavelength measurement apparatus 1 in which thechannel-cut crystal for wavelength measurement is so arranged that X-rayenters the identical cut plane. A channel-cut crystal for collimator 30has a first crystal wall 31 and a second crystal wall 32, and, atrespective crystal walls, a first cut plane 31 a and a second cut plane32 a facing each other are formed. The lengths of respective crystalwalls are shortened in different directions in accordance with thepassing channels of X-ray beams so that a large diffraction angle can beobtained. For a scheme to obtain a large diffraction angle, as shown inFIG. 4, crystals, in which mutual distance is enlarged relative to thelength thereof without shortening the lengths of the crystal wall 31 andthe crystal wall 32, may be employed.

A channel-cut crystal for wavelength measurement 40 has a third crystalwall 41 and a fourth crystal wall 42, and, at respective crystal walls,a third cut plane 41 a and a fourth cut plane 42 a facing each other areformed. In the channel-cut crystal for wavelength measurement 40, acrystal, in which the mutual distances of respective crystal walls 31and 32 are enlarged relative to the lengths of these, is employed so asto obtain a large diffraction angle. These two opposing cut planes 41 aand 42 a are so formed that at least a part of respective projectionsoverlap with the cut planes. This makes it possible to rotate thechannel-cut crystal for wavelength measurement 40 to diffract X-ray inrespective arrangements of (−, +) and (+, −).

In the example in FIG. 3, a rotation center C2 of the channel-cutcrystal for wavelength measurement is set outside the cut plane 41 a.Then, the rotation center C2 is set at a position where X-ray is notshielded by the crystal wall 42 when either of the above arrangementsoccurs and X-ray reaches the cut plane 41 a in either arrangement. Thecut plane 41 a on which X-ray enters when the channel-cut crystal forwavelength measurement 40 diffracts the X-ray in an arrangement of (−,+), and the cut plane 41 a on which X-ray enters when the channel-cutcrystal for wavelength measurement 40 diffracts the X-ray in anarrangement of (+, −) are identical. As described above, the rotationcenter of the channel-cut crystal for wavelength measurement 40 is setat a position that allows X-ray to enter the identical cut plane 41 a inboth cases where X-ray is diffracted in either arrangement of (−, +) or(+, −), therefore absolute wavelength can be measured for highdiffraction angles with high precision. For high diffraction angles,δλ/λ becomes small, therefore high wavelength resolution can beobtained. On this occasion, the cut plane 41 a leads to carry out thediffraction in (−) direction in one arrangement, and the diffraction in(+) direction in the other arrangement.

Next, a method for carrying out X-ray wavelength measurement in theabove-described crystal arrangement will be described. Firstly, twochannel-cut crystals, in which a cut plane has been formed so as to becapable of diffracting X-ray at the identical crystal plane, areprepared from a crystal having a known lattice constant, and these areset on a platform and on the rotatable platform 50 as a channel-cutcrystal for collimator and a channel-cut crystal for wavelengthmeasurement, respectively. The channel-cut crystal for wavelengthmeasurement 40 is so fixed on the rotatable platform 50 that therotation center C2 lies near the crystal wall 41. Firstly, thechannel-cut crystal for wavelength measurement 40 is set to anarrangement for causing (+, −) diffraction, as shown in FIG. 5A.

Then, by guiding X-ray for spectral reflection, firstly, the channel-cutcrystal for wavelength measurement 40 diffracts the X-ray in thearrangement of (+, −) to carry out wavelength measurement. That is,respective channel-cut crystals are arranged so as to be (+, −, +, −) toallow X-ray to be diffracted in the order of cut planes 31 a, 32 a, 41 aand 42 a. On this occasion, in case where the diffraction is carried outby using the identical crystal plane for the channel-cut crystal forcollimator and for the channel-cut crystal for wavelength measurement, asharp peak is obtained when two crystal planes become strictly parallelto each other. As described above, the peak angle position ω₀ of X-rayintensity detected by the X-ray detector 100 is detected with the angledetector 60. The angle position ω₀ is the origin point of thechannel-cut crystal for wavelength measurement.

Next, the channel-cut crystal for wavelength measurement 40 is soarranged as to cause (−, +) diffraction as shown in FIG. 5B. That is,respective channel-cut crystals are so arranged as to cause (+, −, −, +)diffraction, and allow X-ray to be diffracted in the order of cut planes31 a, 32 a, 41 a and 42 a. Then, from the X-ray intensity detected bythe X-ray detector 100 and the angle ω detected by the angle detector60, an X-ray spectrum with high resolution is obtained.

The origin of the angle ω detected by the angle detector 60 in themeasured spectrum is above-described ω₀. Accordingly, the difference inrespective angles ω−ω₀ is the rotation angle of the channel-cut crystalfor wavelength measurement, and Bragg angle θ of the channel-cut crystalfor wavelength measurement on this occasion is represented byθ=π/2−(ω−ω₀)/2. When representing the lattice spacing of the channel-cutcrystal for wavelength measurement by d, the angle θ on the horizontalaxis of a spectrum can be converted to the wavelength λ of X-rayaccording to the formula of λ=2d·sin θ. Further, the wavelength λ (Å) ofX-ray is converted to energy E (eV) according to the formula ofE=12398.419/λ.

The above is described for the case where X-ray to be spectrallyreflected is divergent light, but in case where a spectrum of X-rayhaving been spectrally reflected to some extent or of such parallellight as synchrotron radiation source is measured, the channel-cutcrystal for collimator may be omitted. On this occasion also, bymeasuring ω₀ while arranging the channel-cut crystal for wavelengthmeasurement in (−, +) followed by measuring ω while arranging it in (+,−), as is the case for the above, Bragg angle θ can be calculatedcorrectly.

Embodiment 3

The above-described X-ray wavelength measurement apparatus 1 of theEmbodiment 1 can measure absolute wavelength with high precision, but itis also possible to carry out precise calibration by giving additionalself-calibration function to the angle detector.

FIG. 6 is a side view showing an X-ray wavelength measurement apparatus2 provided with an angle detector having self-calibration function. Asshown in FIG. 6, the X-ray wavelength measurement apparatus 2 includes achannel-cut crystal for collimator 10, a channel-cut crystal forwavelength measurement 20, a fixed platform 49, a rotatable platform 50,a rotary driving instrument 55, an angle detector 60, a controllingsection 70 and a detector 100. The rotary driving instrument 55, theangle detector 60 and the controlling section 70 constitute a rotationcontrol mechanism.

The rotatable platform 50 is connected to the rotary driving instrument55 capable of rotation at intervals of a minute angle. The rotarydriving instrument 55 uses a servo motor, a stepping motor or the like.

The angle detector 60 is a detector for measuring a rotation angle bycounting scales carved to a circular disc 61 with a reading head 63. Theangle detector 60 uses a rotary encoder or the like.

FIG. 7 is a perspective view of the angle detector 60 in the presentinvention. As shown in FIG. 7, the angle detector 60 includes a circulardisc 61 to which scales are carved, a shaft 62 to which the circulardisc 61 is fixed, and a reading head 63 set around the disc at evenintervals. The reading head 63 is arranged around the circular disc 61at even intervals.

The rotatable platform 50, the angle detector 60 and the X-ray detector100 are controlled by the controlling section 70. The controllingsection 70 is constituted of CPU and main memory, and, mainly, carriesout the control of instruments and the calculation of numerical values.

Hereinafter, a method for obtaining the displacement of the scaleposition is described. The displacement of the angle signal of the scalei to be detected by the reading head 63 can be represented as b_(i).Further, the displacement of the angle signal of the scale i+j·N/n atjth reading head 63 can be represented as b_(i+j·N/n). On this occasion,it is intended to indicate the number of reading heads arranged at evenintervals by n, and the number of scales of the encoder by N.

When determining the 0th reading head 63 as the reference head,difference δ_(i,j) between the angle signal b_(i+j·N/n) of the jth headand the angle signal b_(i) of the reference head, and the average valueμ_(i,n) of these can be represented as follows.

δ_(i,j) =b _(i+j·N/n) −b _(i)  (formula I)

$\begin{matrix}{\mu_{i,n} = {{\frac{1}{n}{\sum\limits_{j = 0}^{n - 1}\delta_{i,j}}} = {{\frac{1}{n}{\sum\limits_{j = 0}^{n - 1}b_{i + {j \cdot {N/n}}}}} - b_{i}}}} & ( {{formula}\mspace{20mu} {II}} )\end{matrix}$

The amount resulted from eliminating Fourier components of multiplenumber of n from b_(i) can be obtained as follows.

$\begin{matrix}{{\overset{\sim}{b}}_{i,n} = {{b_{i} - {\frac{1}{n}{\sum\limits_{j = 0}^{n - 1}b_{i + {j \cdot {N/n}}}}}} = {- \mu_{i,n}}}} & ( {{formula}\mspace{20mu} {III}} )\end{matrix}$

The above-described −μ_(i,n) is the displacement of the scale positionof the scale i. In this way, by seeking the measurement differencebetween the reference reading head 63 and respective reading heads andby obtaining the average value thereof, it is possible to calculate thedisplacement of the scale position and to carry out self-calibration. Asdescribed above, it is possible to calibrate the error of such angleinformation as the decentering of an attaching axis under useenvironments and the secular change of the angle detector. In addition,it is also possible to evaluate how much uncertainness is there inobtained absolute wavelength.

Experimental Example

An experiment of wavelength measurement was practiced by using the X-raywavelength measurement apparatus of the Embodiment 1. The experimentalmethod and the experimental results are described below as ExperimentalExample.

As an X-ray source, CuKα line was used, and as a channel-cut crystal, aSi analyzing crystal was used and Si (400) was used as the crystalplane.

Firstly, since the Bragg angle θ is approximately 34.5°, two channel-cutcrystals having a suitable size and figure for the angle were prepared.One of these was fixed on a platform as the channel-cut crystal forcollimator so that diffracted X-ray became approximately parallel to theincident X-ray, and the other was set on a rotatable platform as thechannel-cut crystal for wavelength measurement. The rotation center ofthe channel-cut crystal for wavelength measurement was set so as to liebetween two cut planes.

Then, by setting the channel-cut crystal for wavelength measurement toan arrangement of (+, −) and diffracting X-ray as shown in FIG. 2A, theprofile of the CuKα peak of the X-ray was detected. When an identicalcrystal plane is used for the channel-cut crystal for collimator and forthe channel-cut crystal for wavelength measurement to carry out thediffraction, a sharp peak is obtained when respective crystal planesbecome strictly parallel to each other. The peak angle poison of thechannel-cut crystal for wavelength measurement on this occasion isindicated by ω₀.

Next, by setting the channel-cut crystal for wavelength measurement toan arrangement of (−, +) and diffracting X-ray as shown in FIG. 2B,X-ray wavelength measurement profile with a high-resolution wasmeasured. On this occasion, the channel-cut crystal was set to anarrangement of (+, −, −, +) to cause the diffraction.

The origin of the angle ω detected by the angle detector 60 in themeasured spectrum is the above-described ω₀. Therefore, the differencebetween both angles ω−ω₀ was calculated to obtain the rotation angle ofthe channel-cut crystal for wavelength measurement. Bragg angle θ of thechannel-cut crystal for wavelength measurement on this occasion isθ=(ω−ω₀)/2. When representing the lattice spacing of the channel-cutcrystal for wavelength measurement by d, the angle θ on the horizontalaxis of a spectrum is represented by a formula of λ=2d·sin θ. Accordingto the formula, the angle θ was converted to the wavelength λ of theX-ray. Further, the wavelength λ (Å) of X-ray was converted to energy E(eV) according to the formula of E=12398.419/λ.

FIG. 8 is a profile showing the result of the above-described X-raywavelength measurement. In the graph, ∘ shows the X-ray intensityobtained by the experiment. Each of peaks P1 to P4 shows curve of Lorenzfunction representing peaks of Cukα1 and Cukα2 obtained by calculation,respectively. When subjecting these curves of Lorenz functions tofitting treatment, they coincided with the profile obtained by theexperiment.

Parameters of respective Lorenz functions thus obtained are shown inFIG. 9. The full width of Half Maximum 2.286 eV at the peak P1 is thehighest resolution among those historically obtained. On this occasion,δE is considered to be 0.2 eV or less. Further, precise absolutewavelength of X-ray could be measured.

1. A Method for X-ray wavelength measurement carried out by using achannel-cut crystal for wavelength measurement in which two opposing cutplanes are formed and the lattice constant of which is known, saidmethod comprising the steps of: diffracting X-ray in respectivearrangements of (−, +) and (+, −) with said channel-cut crystal forwavelength measurement; and determining the absolute wavelength of X-rayfrom the difference between crystal rotation angles in said respectivearrangements.
 2. The Method for X-ray wavelength measurement accordingto claim 1, carried out by using a channel-cut crystal for collimatorwhich is arranged on an X-ray incident side of said channel-cut crystalfor wavelength measurement and in which two opposing cut planes areformed, said method further comprising the steps of: diffracting X-rayat a crystal plane having the same index as that of a crystal plane atwhich said channel-cut crystal for wavelength measurement diffractsX-ray at respective cut planes of said channel-cut crystal forcollimator; and guiding the diffracted X-ray into said channel-cutcrystal for wavelength measurement to carry out wavelength measurement.3. An X-ray wavelength measurement apparatus, comprising: a channel-cutcrystal for wavelength measurement in which two opposing cut planes areso formed that at least a part of mutual projections thereof overlapwith the cut planes; and a detector for detecting the intensity of X-rayspectrally reflected by said channel-cut crystal for wavelengthmeasurement, wherein a rotation center of said channel-cut crystal forwavelength measurement is set to be capable of diffracting X-ray inrespective arrangements of (−, +) and (+, −).
 4. The X-ray wavelengthmeasurement apparatus according to claim 3 further comprising achannel-cut crystal for collimator which is arranged on the incidentside of said channel-cut crystal for wavelength measurement and in whichtwo opposing cut planes are formed, wherein said channel-cut crystal forcollimator diffracts X-ray at a crystal plane having the same index asthat of a crystal plane at which said channel-cut crystal for wavelengthmeasurement diffracts X-ray, to guide the diffracted X-ray into saidchannel-cut crystal for wavelength measurement.
 5. The X-ray wavelengthmeasurement apparatus according to claim 3 or 4, wherein saidchannel-cut crystal for collimator is placed so that the rotation can befixed for incident X-ray upon carrying out wavelength measurement. 6.The X-ray wavelength measurement apparatus according to any of claims 3to 5 wherein: the rotation center of said channel-cut crystal forwavelength measurement is set between two cut planes of said channel-cutcrystal for wavelength measurement or between extended planes thereof;and a cut plane on which X-ray is incident when said channel-cut crystalfor wavelength measurement diffracts the X-ray in the arrangement of (−,+) differs from that on which X-ray is incident when said channel-cutcrystal for wavelength measurement diffracts the X-ray in thearrangement of (+, −).
 7. The X-ray wavelength measurement apparatusaccording to any of claims 3 to 5 wherein: the rotation center of saidchannel-cut crystal for wavelength measurement is set in a position thatallows X-ray to enter the identical cut plane when said channel-cutcrystal for wavelength measurement diffracts X-ray in either arrangementof (−, +) or (+, −).
 8. The X-ray wavelength measurement apparatusaccording to any of claims 3 to 7 further comprising a rotation controlmechanism for controlling the rotation of said channel-cut crystal forwavelength measurement, wherein said rotation control mechanism includesan angle detector having self-calibration function for detectingdisplacement of the scale position of a rotation angle.